1. Field of the Invention
The invention relates to a control apparatus and a control method for an internal combustion engine.
2. Description of the Related Art
Japanese Patent Application Publication No. 2003-148225 describes an exhaust gas purification apparatus for a diesel engine that includes a variable valve operating mechanism that changes valve opening characteristics of an intake valve and an exhaust valve. In the above-described apparatus, when the temperature of an exhaust gas purification catalyst is lower than a predetermined value, the amount of internal EGR gas is increased by adjusting a positive or negative valve overlap period. In the above-described apparatus, the temperature of the exhaust gas purification catalyst is increased by the control.
A method, in which combustion is performed at a rich air-fuel ratio in a cylinder (i.e., rich combustion is performed) to increase the temperature of an exhaust gas purification catalyst disposed in an exhaust passage, or to reduce the exhaust gas purification catalyst, is available. When the rich combustion is performed, it is difficult to stabilize the combustion.